Detection of cavitation or gas lock

ABSTRACT

A system and method to identify a condition of cavitation or gas lock in a pump configured to convey a liquid to a surface from a subsurface environment via tubing are described. The system includes a tool to create a binary event based on the condition, the binary event representing a change in state of a parameter. The system also includes a sensor to detect the binary event based on the parameter, and a processor to process output from the sensor to identify the condition.

BACKGROUND

In subsurface production efforts, a pump (e.g., Electric SubmersiblePump or Progressive Cavity Pump) is generally used to bring a liquid(e.g., oil) to the surface. Specifically, a pump in a production wellwill pull the liquid (in some cases the pump carries mostly water, butthe desired “product” can be minerals or gas, and can be produced withother means) into tubing that carries the liquid to the surface. Thepump cannot discriminate between the liquid, and other material (e.g.,sand, dirt, rocks) that may also be pulled into the tubing. When gasenters the tubing or when liquid level drops in the annulus from whichit is being pumped, the lack of fluid in the tubing creates a cavity orvoid (e.g., cavitation or gas lock or vapor lock in the pump). Thiscondition caused by gas or low fluid level can cause damage to the pumpbased on the frequency and duration of its occurrence.

SUMMARY

According to one embodiment, a system to identify a condition ofcavitation or gas lock in a pump configured to convey a liquid to asurface from a subsurface environment via tubing includes a toolconfigured to create a binary event based on the condition, the binaryevent representing a change in state of a parameter; a sensor configuredto detect the binary event based on the parameter; and a processorconfigured to process output from the sensor to identify the condition.

According to another embodiment, a method of identifying a condition ofcavitation or gas lock in a pump configured to convey a liquid to asurface from a subsurface environment via tubing includes creating,using a tool in the subsurface environment, a binary event based on thecondition, the binary event representing a change in state of aparameter; detecting, using a sensor, the binary event based on theparameter; and processing, using a processor, an output from the sensorto identify the condition.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several Figures:

FIG. 1 is a block diagram of a system to identify a cavitation conditionaccording to embodiments of the invention;

FIG. 2 is a cross sectional block diagram of a system to identifycavitation in tubing according to an exemplary embodiment; and

FIG. 3 is a process flow of a method of identifying cavitation in tubingaccording to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

As noted above, cavitation in the production tubing can result in damageto the pump. Thus, awareness of the condition can aid in extending theuseful life of the pump. Currently, flow rate of liquid (e.g., oil)production at the surface is monitored. This monitoring allows anoperator to identify when flow rate has dropped and further investigatewhether the drop in flow rate is due to cavitation. However, a change inflow rate or a particular value of the flow rate is not dispositive, andthe analysis and investigation needed to make a determination mayrequire the pump to be shut off. Embodiments of the systems and methodsdescribed herein relate to a sensor identifying cavitation in the tubingbased on a dispositive or binary event.

As used in the present application, “binary event” refers to an eventthat indicates an objective and discernable switch or change in state ofa parameter. The exemplary binary event detailed below is a change frompositive to negative pressure (pressure to no pressure) for fluid flowof liquid being pumped to the surface. That is, the exemplary binaryevent is a switch in state of the exemplary parameter of pressure. Theexemplary embodiment detailed herein relates to a diverter whoseoperation results in a switch in pressure (from positive to negative)when cavitation occurs in the tubing. This binary event or switch inpressure in the particular embodiment can be detected by a sensor.Alternate embodiments contemplate a different downhole tool than thediverter causing a different dispositive or binary event based oncavitation and a different sensor identifying cavitation based on thatbinary event.

FIG. 1 is a block diagram of a system to identify a cavitation conditionaccording to embodiments of the invention. Generally a tool 5 isdisposed in a downhole environment 2. The tool 5 creates a binarycondition based on cavitation in tubing 20. Although the tool 5 is shownin the tubing 20, embodiments of the system may include the tool 5 beingdisposed on or outside the tubing 20, as well. A sensor 6 identifies thebinary event created by the tool 5. A processing system 7 coupled to thesensor 6 processes the sensor 6 output to automatically take action orprovide information to an operator.

FIG. 2 is a cross sectional block diagram of a system to identifycavitation in tubing 20 according to an exemplary embodiment. Theexemplary embodiment relates to a pressure switch sensor 110, which isan embodiment of the sensor 6, identifying cavitation based on a switchin pressure caused by a diverter 120, which is an embodiment of the tool5, during a cavitation condition. A subsurface environment 2 including aborehole 10 is shown below the earth's surface 1. The borehole 10 may becased and has tubing 20 disposed therein that may be production tubing,for example. The tubing 20 is comprised of sections of tubes withinterfaces 30 between them. In the embodiment of the cavitationidentification system discussed with reference to FIG. 1, a diverter120, discussed further below, is disposed at an interface 30 of the tubesections, and sensor 110 is disposed in the flow of the tubing 20 at thesurface 1. The sensor 110 is coupled to a surface processing system 130,which is an embodiment of the processing system 7. The surfaceprocessing system 130 includes one or more processors 132 processingdata based on instructions stored in one or more memory devices 134 andoutputting the results through an output interface 136. In addition toidentifying cavitation based on data received from the sensor 110, thesurface processing system 130 may perform additional functions relatedto the production effort and may include additional components involvedin that effort.

According to the embodiment shown in FIG. 1, the diverter 120 isdesigned to divert debris such as rocks, sand, and dirt that aresuspended in the fluid out of the (production) tubing 20 and into theannulus 15 between the (cased) borehole 10 and the tubing 20 when thepump 40 is turned off. However, when gas is in the tubing 20 or, foranother reason, fluid levels drop in the tubing 20, the diverter 120according to one embodiment of the invention operates while the pump 40is running. Under these conditions (pump 40 is on and diverter 120 isfunctional), any gas (and fluid) in the tubing 20 will be diverted outof the tubing 20. When fluid levels are sufficiently low in the tubing20 during this procedure, the diverter 120 operation causes pressuredrop in the fluid flow and a vacuum is created at the diverter 120causing fluid to flow in the opposite direction (drop toward the pump).At the pressure switch sensor 110, this change in flow direction of thefluid is seen as a switch from pressure to no pressure (a binary event).As a result, the pressure switch sensor 110 need not be a sophisticatedmeasurement device that measures flow or any particular parameter. Thepressure switch sensor 110 may instead be a check valve that switchesbetween on and off or a pressure valve that switches from positive tonegative pressure to indicate that the cavitation condition has occurredin the tubing 20. The surface processing system 130 coupled to thepressure switch sensor 110 may monitor a length of time that thecondition lasts or a frequency of the condition over a period of time totake automatic action (e.g., shutoff of the pump 40). In alternateembodiments, the surface processing system 130 may provide theinformation indicated by the pressure switch sensor 110 to an operatorthrough the output interface 136 so that the operator determines theaction to take. According to the embodiment discussed with reference toFIG. 1, the diverter 120 includes features described in U.S. Pat. No.6,289,990. In alternate embodiments, the diverter 120 is anotherdiverter that produces the vacuum and subsequent change in fluid flowdirection when it operates while the pump is on during a cavitationcondition.

FIG. 3 is a process flow of a method of identifying cavitation in tubingaccording to an exemplary embodiment of the invention. At block 310,disposing a tool 5 along the tubing 20 includes disposing the diverter120 at an interface 30 between tube sections, for example. The diverter120, according to the exemplary embodiment described above, diverts gaswhile the pump is on such that a vacuum is created. At block 320,positioning a sensor 6 to sense a binary event created by the tool 5includes positioning the pressure switch sensor 110 at the surface 1 inthe flow of the tubing 20. As noted above, the pressure switch sensor110 according to the exemplary embodiment described above may be a checkvalve or pressure valve. Processing the sensor 5 output, at block 330,includes processing system 7 (e.g., surface processing system 130)providing the indication of a cavitation condition to an operator.Alternatively, processing the sensor 5 (pressure switch sensor 110)output includes monitoring the frequency or duration or both of thecavitation condition to determine an action such as, for example,shutting down or slowing down the pump 40.

While one or more embodiments have been shown and described,modifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation.

1. A system to identify a condition of cavitation or gas lock in a pump configured to convey a liquid to a surface from a subsurface environment via tubing, the system comprising: a tool configured to create a binary event based on the condition, the binary event representing a change in state of a parameter; a sensor configured to detect the binary event based on the parameter; and a processor configured to process output from the sensor to identify the condition.
 2. The system according to claim 1, wherein the tool is a diverter configured to divert all materials from the tubing.
 3. The system according to claim 2, wherein the diverter diverts the liquid from the tubing when the gas is in the pump, the gas in the pump creating the condition.
 4. The system according to claim 2, wherein the parameter is pressure, and the binary event is the change in the state of the pressure created by the diverter.
 5. The system according to claim 4, wherein the binary event is a switch from positive to negative pressure in the tubing.
 6. The system according to claim 4, wherein the sensor is a pressure valve or a check valve.
 7. The system according to claim 1, wherein the processor notifies an operator of the condition based on the output from the sensor.
 8. The system according to claim 1, wherein the processor monitors a frequency or duration of the condition based on the output from the sensor to determine an action.
 9. A method of identifying a condition of cavitation or gas lock in a pump configured to convey a liquid to a surface from a subsurface environment via tubing, the method comprising: creating, using a tool in the subsurface environment, a binary event based on the condition, the binary event representing a change in state of a parameter; detecting, using a sensor, the binary event based on the parameter; and processing, using a processor, an output from the sensor to identify the condition.
 10. The method according to claim 9, wherein the tool is a diverter, and the creating the binary event is based on the diverter diverting all materials from the tubing.
 11. The method according to claim 10, further comprising the diverter diverting the liquid from the tubing when the gas is in the pump, the gas in the pump creating the condition.
 12. The method according to claim 10, wherein the parameter is pressure, and the detecting the binary event includes detecting the change in the state of the pressure created by the diverter.
 13. The method according to claim 12, wherein the detecting the binary event includes detecting a switch from a positive to a negative pressure in the tubing.
 14. The method according to claim 9, wherein the processing the output from the sensor includes the processor issuing a notification to an operator indicating the condition.
 15. The method according to claim 9, wherein the processing the output from the sensor includes the processor monitoring a frequency or duration of the condition based on the output from the sensor to determine an action. 